You can do the DLC at any point after the mission select computer opens up. They will be at the bottom side of the globe. Just like any normal level, you can do a free play run after completing the level the first time in storymode if you miss minikits or true hero on the normal playthrough.

And was just wondering if anyone had made any progress on something haven't seen anyone make additional changes since November. I have a capture card and I am more then willing to go ahead and make videos for each level and unlockables in the game. Just checking to make sure someone else wasn't already doing that.